FIG. 9 of (EP-A-0327973, illustrates such a yarn feeder wherein during rotation of the winding-on tube, due to the running motion of the wound-on yarn in relation to the winding on or winding tube and due to centrifugal forces, a forceful air stream exits through the yarn exit of the winding-on tube. This air stream unavoidably carries contaminants and yarn parts which then deposit at the yarn feeder and in the surrounding areas. In a bracket extending alongside the storage drum opto-electronic sensors are received and desire information from the motion of the yarn and/or presence or absence of the yarn in detection zones for controlling the winding-on drive and for further control functions. There opto-electronic sensors mostly operate with light reflection. In the known yarn feeder (EP-A-0327973, FIG. 9) among others, an opto-electronic sensor is provided in a sensor housing received in the bracket and aligned with a winding-on region of the storage drum in order to scan the frontmost yarn windings and to e.g. detect and signal a yarn breakage. The light inlet/exit zone of the opto-electronic sensor, e.g. a window, is imparted by the contaminated air stream when the yarn-winding-on tube is rotating. The contaminants unfortunately tend to deposit on the light inlet/-exit zone and cause deterioration of the optical scanning properties thereof. The same problem also occurs with opto-electronic sensors provided which are at a greater distance (in the axial direction of the storage drum) downstream of the yarn exit. In order to guarantee the operational reliability of the opto-electronic sensors, frequent cleaning operations are needed, e.g. by sweeping or with pressurised air.
It is a task for the invention to create a yarn feeder of the above type in which the operational reliability of the opto-electronic sensors is guaranteed for long operating durations, or in which time periods between cleaning cycles are considerably extended.
This task can be achieved by providing a wind or air deflector between the yarn exit and the light inlet/exit zone.
The air stream exiting the yarn exit is hindered by the wind deflector from depositing the contaminants therein at the light inlet/-exit zone which, therefore, remains free of contaminants or requires cleaning operations only in considerably extended time periods. The contaminants either pass the light inlet/-exit zone without depositing there, or are collected at a side of the wind deflector remote from the light inlet/-exit zone where they are of no harm and are removed in irregular time periods by the air stream itself.
It is suitable to arrange the windows constituting the inlet/-exit zone leeward of the wind deflector to hinder the deposit of contaminants. Since in most cases the yarn feeder is installed with its bracket on top, nevertheless contaminants passing the wind deflector are automatically removed from the leeward side by gravity or are conveyed by gravity into the air flow moving past the light inlet-exit zone, and are removed then.
In order to avoid the deposit of contaminants which are sidewardly deviated, the wind deflector is provided which has a length greater than the width of the light inlet/-exit zone.
The wind deflector according to the invention is structurally simple, and is provided at the lower side of a sensor housing, and is preferably unitary with this lower side. The lower side of the sensor housing may also contain the light inlet/-exit zone in the form of a window.
In a structurally simple fashion, the above task can be fulfilled by a wind deflector which is designed as a straight wall essentially radially oriented in relation to the axis of the storage drum. It is also possible to design the wind deflector as an inclined wall which is arranged counter to or in the flow direction of the air stream, and/or provide the wind deflector with a saw-tooth or curved cross section.
The function of maintaining the light inlet/-exit zone in a clean condition is further improve when the wind deflector has a V-or C shaped form. The height of the wind deflector should essentially correspond to the width of the light inlet/-exit zone. The distance between the wind deflector and the light inlet/-exit zone may be smaller than the height of the wind deflector. In case that the free edge of the wind deflector is formed as a flow break off edge, the air stream advantageously will leave the wind deflector rapidly and contaminants cannot be deposited at the light inlet/-exit zone. In order to accordingly equip yarn feeders which are currently with such a wind or use deflector, the wind deflector may constitute a plastic or metal form part which can be attached at the sensor housing, e.g. by gluing, soldering, screwing or riveting.